The failure to detect, find and correct minor roof deterioration in the earliest stages is considered the greatest cause of premature roof failure. This is particularly true of roofing materials applied on low-slope or flat roofs. Costly roofing problems are often the result of design deficiencies or faulty application of the roof system. Even when properly designed and applied, all roofing materials deteriorate from exposure to the weather at rates determined largely by the kind of material and the conditions of exposure.
The failure to detect water accumulation, locate the source of water ingress and perform proper repairs in early stages is considered the greatest cause of premature roof failure. Low slope roofing systems are vulnerable to undetected moisture ingress for three reasons:                a—Hydrostatic pressure on top of membrane from low structural sloping.        b—Difficulty identifying trade damage and defects during construction.        c—Presence of a vapor barrier at the bottom of the roofing system assembly.        
If trade damage and defects in the membrane are not identified and corrected during construction water can ingress into the rigid insulation and accumulate on the vapor barrier. Because the vapor barrier is impermeable water ingress into occupied spaces of the building does not occur causing undetected water accumulation for extended periods of time. Undetected water accumulation can lead to; structural deterioration of buildings, negative impacts to building occupants from mold growth and creation of favorable environments for pests. Water ingress must be identified and repaired to prevent damages from water accumulation.
Water ingress detection systems have been developed to locate and repair roof leaks before damages become irreversible. The detection systems are installed on the vapor barrier so that water ingress from defects in the membrane, water vapor mass transport and defective roof accessories can be detected. By installing a leak detection system on the vapor barrier locating the source of the water ingress can be difficult due to lateral movement of the water as it passes through joints in the cover board and rigid insulation. The detection system must locate any membrane breach through the membrane and intervening layers to the vapor barrier or deck surface.
Several methods have been used to try and locate roof leaks after they have occurred. Precisely locating defects and or breaches the becomes a particular problem for conventional roofing systems where the roof membrane is located at the top of the assembly and any leak detection system is placed below the membrane on top of a vapor barrier above the structural deck. The detection system must then locate any membrane breach through the membrane and intervening layers to the vapor barrier or deck surface.
A roof leak monitoring system is detailed in U.S. Pat. No. 7,652,481 (Vokey) issued Jan. 26, 2010 to Detec Systems LLC discloses an arrangement for leak detection on flat roof systems using a gridded system of wire sensors whereby the X and Y wires that form a grid are alternately operated as an electric guard and then as a leak detection sensor measuring the conductivity to ground at a membrane breach through the water on the surface of the membrane. Although fundamentally different in its detection measurement, the method relies on the assumption that a breach through the membrane will be located coincidentally at an intersection of the x and y wires of the common grid section. However, where there are two breaches including a first breach close to an x grid location only and a second breach at a location next to a y grid location only can, the analysis of the voltages can result in an incorrect assessment that there is a single breach in the grid sections where the x and y wires of the grid intersect.
An improvement to this arrangement is also shown in U.S. Pat. No. 8,319,508 (Vokey) issued Nov. 27 2012.
A yet further improvement is shown in Published US application 2014/0361796 which shows that, where a roof deck is used which has no or low electrical conductivity, a measurement system can be provided where the current is detected between a sensor on top of the membrane and a conductive layer underneath the membrane connecting the deck to the membrane such as an adhesive.
The disclosure of the above Vokey patents may be referred to for further details of the subject matter claimed herein.